The present invention relates to improvements in metal halogen battery systems. More particularly the invention relates to a new multiple stage, multiple filter hydrate store for these battery systems.
The electrical energy storage systems of the type referred to herein (e.g., a zinc chlorine battery system or other metal-halogen battery system) utilize a halogen hydrate as the source of halogen components for reduction at a normally positive electrode, and an oxidizable metal adapted to become oxidized at a normally negative electrode during the normal discharge of the storage system. An aqueous electrolyte is employed for replenishing the supply of the halogen components as it becomes reduced at the positive electrode. The electrolyte contains the dissolved ions of the oxidized metal and the reduced halogen and is circulated between the electrode area and a storage area containing halogen hydrate, which progressively decomposes during a normal discharge of the electrical energy system, liberating additional elemental halogen to be consumed at the positive electrode.
The state of the art in electrical energy storage systems or battery systems of this type is described in the following cited references owned by the same assignee as the present invention, such as Symons U.S. Pat. No. 3,713,888 entitled "Process For Electrical Energy Using Solid Halogen Hydrates"; Symons U.S. Pat. No. 3,809,578 entitled "Process for Forming and Storing Halogen Hydrate in a Battery"; and Bjorkman U.S. Pat. No. 3,814,630 entitled "Filter/Store For Electric Energy Storage Device"; and, in commonly assigned copending Bjorkman U.S. patent application Ser. No. 358,628, filed Mar. 16, 1982, entitled "Metal Halogen Battery System With Multiple Outlet Nozzel For Hydrate."
The specific teachings of the aforementioned cited references are incorporated herein by reference. The new multiple state, multiple hydrate store disclosed herein is particularly useful for application in a battery system of the type described in the copending application referred to immediately above. However, it also has wide application for use in numerous metal halogen battery systems.
The basic operation of a zinc chloride battery system is as follows. In charge, an electrolyte pump delivers aqueous electrolyte to pockets between pairs of porous graphite-chlorine electrodes in a battery stack comprised of a plurality of cells. The electrolyte passes through the porous chlorine electrodes into a chamber between opposite polarity electrodes, flows up between the electrodes, then flows back into the battery sump. Chlorine gas liberated from porous graphite electrode substrates is pumped by a gear pump, otherwise referred to as the gas pump, and before entering the gas pump, the chlorine is mixed with electrolyte chilled by a chiller unit. The chlorine and chilled electrolyte are mixed in the gear pump, chlorine hydrate forms in a process analogous to the water freezing process with chlorine included in the ice crystal, and the chlorine hydrate-electrolyte mixture is deposited in the store. In discharge, chlorine is liberated from the hydrate by decomposition of the chlorine hydrate in the store in a process analogous to the melting of ice, by injection of warm electrolyte for the sump. On development of the required chlorine gas pressure in the store, the chlorine is injected and mixed with and dissolved in the electrolyte, which is then fed to the porous electrodes in the battery stack. The battery stack is then discharged, wherein the electrode dissolution of zinc occurs at the zinc electrode, reduction of the dissolved chlorine occurs at the chlorine electrode, power is available from the battery terminals, and zinc chloride is formed in the electrolyte by reaction of zinc and chlorine to form zinc chloride.
Further discussion of the structure and operation of zinc chloride battery system may be found in commonly assigned copending U.S. patent applications of Fong et al., Ser. No. 310,627, filed Oct. 13, 1981, entitled "Metal Halogen Battery Construction With Improved Tehchnique For Producing Halogen Hydrate"; of Kiwalle et al., Ser. No. 343,904, filed Jan. 29, 1982, entitled "Metal Halogen Battery System," and of Hacha, Ser. No. 357,742, filed Mar. 12, 1982, entitled "Halogen Hydrate Storage Device for Mobile Zinc-Chloride Battery Systems." Such systems are also described in published reports prepared by the assignee herein, such as "Development of the Zinc-Chloride Battery for Utility Applications," Interim Report EM-1417, May 1980, and "Development of the Zinc-Chloride Battery for Utility Applications," Interim Report EM-1051, April 1979, both prepared for the Electric Power Research Institute, Palo Alto, Calif. The specific teachings of the aforementioned cited references are incorporated herein by reference.
During the development of the zinc-chloride battery system, several single stage filter designs for use in the hydrate store have been tested, including a rectangular filter across the top of the store, an L-shape filter across one side and the bottom of the store, a combination of these two filters in a single stage, a basket-type filter seated in the store, and a bag like filter substantially overlying the interior walls of the store (as described in U.S. Pat. No. 3,814,630). The purpose of the filter in the hydrate store is to separate the compressible particulate chlorine hydrate from the liquid used in the hydrate formation process. As the chloride hydrate enters the store, it is in the form of a dilute slurry, of which approximately seven (7) percent is hydrate crystal. However, due to the amount of chlorine gas which is liberated during the charging of the battery, it is not practical to store the chlorine hydrate particles in this dilute slurry. Accordingly, a filter is used to provide a hydrate consentration system for removing as much of the excess liquid as possible. It will be appreciated that the increase in the density of the hydrate particles in the store will result in a decrease in the size and weight of the battery system. This advantageous result is particularly important where the battery system is employed in a battery-powered vehicle.
Accordingly, it is a principal object of the present invention to provide a multiple stage, multiple filter hydrate store for a zinc-chloride battery system which more effectively concentrates the chlorine hydrate particles during the charging of the battery system.
It is a more specific object of the present invention to provide a hydrate store filter design having three separate sections and which operates in three discrete stages to achieve a substantially uniform liquid flow through the store during the charging of the battery system while maintaining a hydraulically compressive load on the hydrate.
It is an additional object of the present invention to provide a multiple stage, multiple filter hydrate store filtration or hydrate concentration system which is adapted to maintain the pressure in the hydrate store within acceptable levels during the charging of the battery.
Additional advantages and features of the present invention will become apparent from a reading of the detailed description of the preferred embodiments which makes reference to the following set of drawings in which: